1. Field of Invention
The invention relates to fall arrest systems and more particularly to a safety hook for fall arrest system with improved characteristics.
2. Description of Related Art
A great variety of systems are used for purposes of arresting a person's fall. A person working at dangerous heights may be supported by a lanyard looped around on his or her waist. The lanyard is attached to a ring of a safety hook by looping. The safety hook further has a hook portion so that one end of a steel wire can be releasably fastened at the hook portion and the other end thereof extends to secure to a proximate support structure. The safety hook thus can prevent the person from falling.
A conventional safety hook for fall arrest system is shown in FIGS. 1 to 5. The safety hook comprises a hook body A including a locking dog A5 at one end, a ring A6 at the other end for permitting a lanyard (not shown) to loop around, a first pivot A2 in an intermediate portion of the hook body A, a second pivot A3 proximate to the ring A6, an opening A1 between one end and the second pivot A3, and a recess A7 in the back of the intermediate portion of the hook body A opposite the opening A1.
The safety hook further comprises a groove-like latch member B of U cross-section at the back of the hook body A, a first torsion spring D mounted between an inner surface of a joining portion of the latch member B and the first pivot A2, and a pin B1 fixedly secured to the latch member B and slidably disposed in a slot A4 of the hook body A, the pin B1 having an enlarged head disposed externally of the latch member B so that the latch member B is pivotal about the first pivot A2.
The safety hook further comprises a lock member C. The lock member C is a groove-like member and has two substantially triangular side walls C2 partially straddle the intermediate portion of the hook body A. The lock member C is assembled with the hook body A by means of the second pivot A3. A second torsion spring E is mounted around the second pivot A3 between an inner surface of the groove portion of the lock member C and the intermediate portion of the hook body A so that the lock member C may be pivotal about the second pivot A3.
Each side wall C2 has a detent C3 at a corner. The detents C3 are rested upon the pin B1 when the safety hook is closed. A through hole C1 is formed on the groove portion of the lock member C distal the second pivot A3. The locking dog A5 is inserted into the through hole C1 when the safety hook is locked (see FIG. 4).
For opening the safety hook, a person may clockwise pivotably push an upper portion of the latch member B. Hence, the first torsion spring D is compressed (i.e., elastic energy being stored) and the pin B1 slides from one end of the slot A4 toward the other end thereof. The pushing will be stopped when the pin B1 reaches the other end of the slot A4 (see FIG. 5). The detents C3 are thus not stopped by the pin B1.
Next, the person may counterclockwise pivotably push the lock member C to disengage the through hole C1 from the locking dog A5 with the second torsion spring E being compressed (i.e., elastic energy being stored). The pushing will be stopped when the groove portion of the lock member C contacts the hook body A. As a result, the safety hook is open (see FIG. 5).
For closing the safety hook, the person may release the lock member C and the energized lock member C thus automatically returns to its locked position with the locking dog A5 inserted into the through hole C1. Next, the person may release the latch member B and the energized latch member B thus automatically returns to its locked position with the pin B1 being disposed at one end of the slot A4 (see FIG. 4).
However, the well known safety hook is disadvantageous because the hook opening and closing mechanism is complicated. It is often that the safety hook may jam after a short period time of use. This is not a safe design. Thus, the need for improvement still exists.